1. Field of the Invention
The present invention relates to a method for producing an optical information recording medium, and more particularly, to a method for producing an optical information recording medium that includes a disc-shaped resin substrate having a peripheral edge disposed with an non-recording region.
2. Description of the Related Art
A CD-R is a writable, optical information recording medium (optical disc) on which information can be written only once by irradiation with laser light, and is widely known. CD-Rs are advantageous in that, in comparison with conventional CDs in which information is recorded by forming pits on a substrate by injection molding, a small number of CDs can be manufactured rapidly and at a reasonable cost. Moreover, the demand for CD-Rs has been escalating recently with the spread of personal computers.
CD-Rs typically comprise a transparent disc substrate having successively disposed thereon a recording layer formed of an organic dye, a metallic (e.g., gold) reflective layer, and a resin protective layer. Information is recorded on the optical disc by irradiating the optical disc with a laser in the near infrared region (ordinarily laser light having a wavelength in the vicinity of 780 nm). Specifically, the portion of the dye recording layer that is irradiated absorbs the light, whereby temperature increases at the irradiated portion. The local increase in temperature deforms the recording layer (e.g., to form pits) at the irradiated portion, whereby information is recorded. The recorded information is ordinarily reproduced by irradiating the optical disc with a laser having the same wavelength as that of the laser used to record the information, and by detecting a difference in reflectance between the region of the recording layer that has been thermally deformed (recorded portion) and the region of the recording layer that has not been deformed (unrecorded portion).
Recently, writable digital versatile discs (DVD-Rs) have also been put to practical use as media having a larger recording capacity than CD-Rs. DVD-Rs typically comprise two transparent disc substrates that each have successively disposed thereon a recording layer formed of an organic dye, a reflective layer, and a resin protective layer, with the discs being adhered together so that the recording layers face inward, or comprise the transparent disc substrate and a protective substrate having the same disc shape as the disc substrate that are adhered together. In each transparent disc substrate, there is formed a guide groove (pre-groove) for tracking laser light irradiated during recording. The pre-groove has a width (0.74 to 0.8 μm) that is equal to or less than half the width of the pre-groove of a CD-R.
The outer peripheral edge of a CD-R or DVD-R is a non-recording region where no dye recording layer is disposed. The purpose of the non-recording region is to improve the outer appearance of the disc by covering the dye recording layer with the reflective layer, and to enhance adhesion by directly adhering the protective layer to the substrate. The dye recording layer is formed by spin-coating a dye solution onto the surface of the substrate and drying the dye solution. However, although it is possible to initiate spin coating so that the spin coater begins coating from a somewhat limited position at the inner periphery of the substrate, it is difficult to control the range of coating towards the outer periphery. For this reason, the dye recording layer is generally first disposed on the entire surface of the substrate, and then cleaning solution is jetted onto the dye recording layer at the outer peripheral edge to remove the dye recording layer from the outer peripheral edge and create the non-recording region.
There are generally two ways that the non-recording region is formed in this manner during the process of producing the optical disc. One is by washing/removing the dye recording layer immediately after it has been formed, and the other is by washing/removing the dye recording layer after both it and the reflective layer have been formed. Below, the former may be called “earlier washing” and the latter may be called “later washing”.
In the case of earlier washing, there are problems in that droplets of the cleaning solution may be scattered onto portions of the recording layer that are not to be removed, whereby those portions are dissolved and recording errors occur at those portions during recording or playback.
In the case of later washing (i.e., when the dye recording layer is formed by spin-coating the dye solution onto the surface of the substrate and allowing the dye solution to dry, and washing is conducted after the reflective layer is formed only on the recording region of the dye recording layer), the non-recording region is formed by washing only the portion of the recording layer disposed at the outer peripheral edge, where the reflective layer is not formed. However, practical problems arise in that the shape of the edge of the recording layer may become irregular depending upon washing conditions. In addition, because time lapses after coating the dye recording layer, there is the problem that it takes time wash the recording layer.
It is possible to prevent the cleaning solution from being scattered and adhering to the dye recording layer by preforming the non-recording region by spin-coating the dye solution onto the surface of the substrate except for the outer peripheral edge and allowing the dye solution to dry to thereby form the dye recording layer, and then washing after the reflective layer has been formed on the dye recording layer. However, because it is difficult to control the range of coating towards the outer periphery of the substrate, the dye recording layer intrudes into the area where the substrate and the reflective layer should ordinarily be closely adhered together, which reduces adhesion between the substrate and the reflective layer. When adhesion is reduced in this manner, water or oxygen may intrude from outside into the dye recording layer, whereby storage stability of the recording medium is reduced.